Question 13 Roman to Integer

The description of the question is in the following link:

https://leetcode.com/problems/roman-to-integer/

My Code:

class Solution:
    def romanToInt(self, s: str) -> int:
        RomanToIntegerDict = {
            "I": 1,
            "V": 5,
            "X": 10,
            "L": 50,
            "C": 100,
            "D": 500,
            "M": 1000,
        }
        if len(s) ==1:
            return RomanToIntegerDict[s[0]]
        else:
            OutputNum = 0
            i = 0
            while i< len(s):
                if i == len(s) -1:
                    OutputNum += RomanToIntegerDict[s[i]]
                    return OutputNum
                else:
                    KeyThis = s[i]
                    KeyNext = s[i+1]
                    if RomanToIntegerDict[KeyThis]< RomanToIntegerDict[KeyNext]:
                        OutputNum += RomanToIntegerDict[KeyNext]-RomanToIntegerDict[KeyThis]
                        i+=1
                    else:
                        OutputNum += RomanToIntegerDict[KeyThis]
                    i+=1
            return OutputNum

Explanation: the key point is to know how to read the roman number. Whenever the number behind you is larger than the value you have now, it means that you need to take the subtraction between the number later and the number you have now. Next point is to be careful with the last element in the string.